Process for reduction of nitroolefins



Patented Apr. 28, 1953 UNITED STATES PATENT OFFICE PROCESS FOR REDUCTION OF N ITROOLEFIN S John B. Tindall, Terre Haute, Ind., assignor to Commercial Solvents Corporation, Terre Haute, Ind, a corporation of Maryland No Drawing. Application May 11, 1949, Serial No. 92,731

in which R may be either alkyl or aryl.

This case is a continuation-in-part application of my application, U. S. Serial No. 563,096, filed November 11, 1944. g

Nitroolefins of the above general type have previously been reduced in accordance with a variety of procedures, some of which have involved electrolytic reduction; reduction with nascent hydrogen, i. e., utilization of mixtures such as iron and hydrochloride acid; reduction with molecular hydrogen in the presence of noble metal catalyst and a mineral acid, etc. While all of the aforementioned methods can be utilized for the reduction of nitroolefins, none of them is free from certain material disadvantages. For example, with procedures involving electrolytic reduction, the yields of the desired products are quite low. Certain of the methods are capable of reducing only specific types of nitroolefins in: cluded by the above general formula while still other procedures involving the use of noble metal, catalysts and mineral acids, although rather effective, have two marked disadvantages from the standpoint of their commercial application, i. e.,. the type of catalyst required for such procedures is very expensive and. the presence of mineral acids in the hydrogenation apparatus presents serious corrosion problems. Furthermore, although catalytic reduction has been effected in accordance with the procedure just mentioned, no one, to my knowledge, has ever been able to reduce nitroolefins successfully in the presence of a nickel catalyst. In all prior attempts of which: I am aware certain bimolecular compounds and/or intractable polymeric materials were obtained.

It is an object of my invention to provide a method for reducing nitroolefins of the above type which is readily adaptable to commercial production and which is capable of giving a comparatively high total yield of amines and ketones.

12 Claims. (01. 260570.8)

It is a further object of my invention to provide a process for the reduction of such nitroolefins whereby the reaction may be conveniently controlled to produce the corresponding amine in predominant amounts. The reaction may also be controlled toproduc the corresponding ketone in predominating amounts according to the procedure described in my co-pending application, U. S. Serial No. 92,732, filed of even date herewith.

Other objects will be apparent from the description which follows:

I have now discovered that the above and other objects may be accomplished by subjecting nitroolefins of the aforesaid type to the action of molecular hydrogen in the presence of Fancy nickel catalyst and an organic acid. In accordance. with my invention, a mixtur comprising the desirednitroolefin, Raney nickel catalyst, and an Y organic acid is charged to a suitable hydrogenation apparatus and subjected to a hydrogen pressure ranging from 500 to 2000 pounds at temperatures of between 30 and 100 C. Suitable organic solvents may also be used in the reaction medium if desired.

The above reduction is effected in a substantially anhydrous medium if the amine is to be produced in predominating amounts over the ketones. I have found that such object may be realized by the utilization of an organic solvent medium which is maintained in an anhydrous condition or at least which is initially anhydrous. The latter limitation is mentioned because of the fact that the reaction involved, i. e., reduction of a nitroolefin to the corresponding amine, of necessity, results in the liberation of varying amounts of water, and, therefore, as the reduction proceeds, the concentration of water in the reaction mixture increases. While, as may be inferred from the above, the presence of water in the reaction mixture is undesirable, When the amine is the preferred product, such water of reaction does not appreciably interfere with the procurement of amine in predominating amounts.

Also, it may be mentioned in this connection that another factor tending to influence the final composition of the reduction mixture is the strength of the acid utilized. If a small amount of water is present in the reaction medium and a preponderance of the amine is desired, I have found that this object can be realized by utilizing organic acids having dissociation constants not substantially higher than that of acetic acid, 1.86 10 If the reaction medium is substantially anhydrous, however, any organic acid having an ionization constant between about 1.4 10- and 1.1 can be used. Examples of organic acids which can be used to give a preponderance of amines, even in the presence of very small amounts of water, are acetic, propionic, butyric, 'valeric, and the like. Examples of organic acids which can be used to give a preponderance of amines when the reaction medium is anhydrous include lactic, tartaric, formic, and the like, in addition to those listedabove. The quantity of acid employed can vary, and has'been found to be not particularly critical, with the exception that at least about one 'mole of acid should be used for each mole'of nitroolefin to'be reduced. The term organic acid as applied to my invention does not include the halogen derivatives of the organic acids such as chlorpropionic, brom propionic, and the like even though some of such derivatives have dissociationconstants within the range specified, due to the harmful effect ofthe halogen on the catalyst.

*From the above it can be: seen that several variables affect the proportion of amine formed relation to ketone. Thus amine formation is favored by the substantial-absence of water, and by weal: acid conditions. The latter. can be controlledeither byusing'a weak organic acidin the medium or a weaker a stronger-acid. in the absence of a solventlin which it can ionize.

The explanation for the effect of these variables probably lies in the nature of the reaction involved, although I do not wish to be limitedto any particular theory of operation. I -have found that when nitroolefins are reduced in accordance with my invention, the first reactionoccurring-is the'formation of hydroxylamines. It is understood, however, that simultaneously withthis reaction small quantities of. nitroolefinsarealso reduced directly to form the amine. Upon further reduction, the hydroxylamine is rearranged to form an oxime. It is at this stageith-at'the. conditions mentioned above either favor the-formation of a'ketone or an amine. :Whether. the ke tone or amine is then formed in predominating amounts depends upon whether ornotthe'reaction conditions favor hydrolysis ofthe oxime. If the conditions do not favorhydrolysis or the. oximes to form ketones, the oxime is, upon further reduction, converted into the corresponding amine. Accordingly, therefore, if the medium contains a strong organic acid (an organicacld with a dissociation constant between about 1.86 10- and 1.1 l0- such an acid; when dissolved in an inert solvent in which it can ionize, tends to cause hydrolysis of the oxime to give a greater proportion of ketone. Likewise, if a Weaker acid is used in the medium, and sufficient water is present to cause the weakacid to become very active by ionization, hydrolysis is favored with an accompanying increase in ketone. production. The converse of the variables is also true; that'is, if a weak acid is used, or a strong acid in the absence of water, a predominant amount of the amine is formed. It is understood, however, that amine formation is favored even though a strong acid is used,.provided theretis no solvent (either water orv organic solventipresent in which the acid may ionize.

Some amines aretalways'. formed duringithe reduction, even under conditions most favorable to hydrolysis, partly because the nitroolefincan be-reduced directlyto the amine, .and partly because some of the oxime is reduced to'the amine even under the adverse. conditions. Likewise, some ketone is always formed, evenimder. condi- 4 tions adverse thereto, because sufiicient water is liberated during the reaction to cause at least a small portion of the acid to ionize, thus causing hydrolysis of a small portion of the oxime to ketone.

If'the reduction of the nitroolefins is carried "out inl'th-e absence of an organic.acid,.under either neutral or basic conditions, the yields of both :amines and ketones are substantially reduced.

Thepresence of the organic acid is necessary in .orclerzto eliminate or minimize the formation of undesirable condensation products, which otherwise will beproduoed in predominating amounts. Inorganic. acids cannot be used in my process due to their tendency to poison the Haney nickel cata- .lyst.

.Nitroole'fins which are satisfactorily reduced in accordance with my invention are represented by the following general structural formula:

in which R, is either. alkyl or aryl. Examples of nitroolefins coming within the above formula, which can be reduced according to, my invention, include, l-phenyl-Z-nitro v1 butene, 1 (p-isopropylphenyl) 2- nitropropene, 1 (m-tolyl) -2- nitro-propene, 2--nitro-2-hexene, l-phenyl-Z-nitro-l-propene, 4-pheny1-2-nitro-2-pentene, 1- (pmethoxyphenyl) -2-nitropropene.

Solvents suitable for use in the medium in my process include a wide variety of organic solvents. Any organic solvent which is inert to the reactants and products at the conditions ,employed is satisfactory for use, in my process. .Examples of solvents coming withinthe above definition include a wide variety of. alcohols, ethers, estersacids and hydrocarbons, suchas methanol, ethanol, propanol, ethyl ether, propyl ether, ethylhexylether, methyl acetate, ethyl formate, amyl acetate, hexadecane, andthe like.

.If a substantially water-insoluble solvent is used, even. inthe absence of waterother than that formed by the reaction, the ketone is produced in. larger quantities than is the amine.

When the reaction appears to be complete, the reduction mixture iswithdrawn from the hydrogenation apparatus and the crude product refined by various methods, depending on the initial composition ofthe reaction mixtureused. In'general, the reaction mixture is acidified with hydrochloric acid or sulfuric acid andthe extraneous materials removed by distillation. The non-basicoil is..then. separated from the residue byextraction withbenzene or asimilar solvent and the. resultant. extract distilled to recover the ketone. The. amine, which is presentin the aqueousportion of the reaction mixture in the form. of its inorganic salt, is liberated by the addition of a-suitable base, such as sodium hydroxide. The amine thus liberated is then removed from .the aqueous mixture by extraction with benzene and the benzene extract fractionally distilled to obtain the substantially pure amine. In certain instances, it may be found desirable to separate. the. amine from the aforesaid alkaline aqueous mixture, by steam distillation.

My .inventionlmay be furtherillustrated by the following specific examples.

EXAMPLE, I

vA mixture consisting of 250g. (1.53 mols) of 1-phenyl-2enitro-l-propene, cc. (1.48 equivalents), of acetic acid, 600 cc. of methanoland 20 g. of Raney nickel catalyst was placed in a rock-j the art. 1 In general, it may be said that any process involving the reduction of nitroolefins of the aforesaid type to their corresponding amines and ketones in which the amines are produced in predominating amounts, by liquid phase hydrogenation in the presence of Raney nickel catalyst and an organic acid of the type described, lies within the scope of my invention.

I claim:

the form of methyl acetate. Distillation was con- 10 I a Process for the reduction of nitrooleflns tinued until the oily-appearing liquid ceased to of the type: come over. The oil layer thus obtained consisted f of phenylacetone and amounted to 9.8 g. corre- RC=Calkyl sponding to ayield of 4.7% based on the l-phenylwherein R represents a member selected from Z-nitro-l-propene used. The residue from the the group consisting of alkyl, phenyl, alkyl subdistillation was decanted off and made alkaline stituted phenyl and alkoxyphenyl, to produce a With Sodium ydroxide. An oil layer for d On mixture of amines and ketones containing a the addition of the base and was separated. The predominant proportion of amines, the improveremaining water layer was then extracted with 7 ment which comprises subjecting a mixture conbenzene and the combined oil layer and benzene sisting of a nitroolefin 0f the aforesaid type, an extracts were fractionated. After the water and inert organic solvent other than a water-insoluble benzene had been removed, 1 .1 of solvent, and an organic carboxylic acid having -p y -p p boiling at 105 C. (35 mm.) an ionization constant at 25 C. of between about was obtained. This yield corresponded to 60% 1,4 X 10- d 1,36 10- and1ess t about of the theoretical- 25 1 mole of water per mole of nitroolefin, to the action of molecular hydrogen in the presence of EXAMPLE II Raney nickel catalyst at elevated pressure. A mixture consisting of 1 of t 2. In a process for the reduction of nitroolefins hexene, 60 cc. of acetic acid, 700 cc. of methanol of the type: and 20 g. of Raney nickel catalyst was placed in R a rocking bomb hydrogenation unit and reduced RC=Ca1 y at 1000 pounds pressure at temperature which wherein R represents a member selected from varied from 30 to 82 C. The reaction required the group consisting of alkyl, phenyl, alkyl subthree hours for completion. At the end of the stituted phenyl and alkoxyphenyl, to produce a reduction, the product was filtered and 90 cc. of mixture of amines and ketones in which the hydrochloric acid added. The mixture was then amine is present in predominant amounts, the distilled, taking off methyl acetate and excess improvement which comprises subjecting a mixmethanol. After the first methanol fraction had ture consisting of a nitroolefin of the aforesaid come off, 500 cc. 1 of water was added. Distiltype, an inert organic solvent other than a lation was continued until the oily-appearing water-insoluble solvent, and an organic carliquids stopped coming over. The oily-layer boxylic acid having an ionization constant at 25 amounted to 29 cc., containing 24.2 g. of 2-hex- C. of between about 1.4 X 10 and 1.86 X 10* anone. This corresponded to a yield of 25.3%. and less than about 1 mole of water per mole of To the residue from the distillation was added nitroolefin, to the action of molecular hydrogen 60 g. of sodium hydroxide and 200 cc. of water. 5 in the presence of Raney nickel catalyst at tem- This mixture was then refluxed until free from peratures between about and 100 C. and at the odor of ammonia. Upon further distillapressures between about 500 and 2000 pounds per tion, two layers of the distillate were formed. square inch. The water layer dissolved in the oil upon agita- 3. The process of claim 2 wherein the nitrotion. The total volume of the distillate was 123 olefin is 1-phenyl-2-nitro-1-propene. 00., containing 50 g. of Z-amino-hexane. This 4. The process of claim 2 wherein the nitrocorresponded to a yield of 51.7%. olefin is 2-nitro-2-hexene.

In the following table, the results of a series 5. The process of claim 2 wherein the nitrooleof reductions of 2-nitro-1-phenyl-1-propene are fin is l-(p-methoxyphenyl)-2-nitropropene. given. Each of these reductions was carried out 6. In a process for the reduction of nitroexactly according to the procedure described in olefins of the type: Example I except that varying solvents, acids, 1 and quantities of reactants were used. R-C==Calkyl Table I Wt. of Phenylsolvent and Acid and Yield of Yield of Total Run $5221., (P125335?) (E1222?) (r r g t) Grams 20o Methanol600. Acetic75 48.8 12.0 60.8 200 Butanol600 Acetic-40"-.. 45.2 21.0 66.2 22.8 8.5 31.3 25.2 6.1 31.3 60.0 4.7 64.7 250 d d0 59.0 3.9 2- 200 Methanol300 Formic 35.6 33.2 68.8 200 None Acetic600.... 44 .0

It is to be understood, of course, that my inwherein R represents a member selected from the vention is not to be construed as limited to the group c s sting of alkyhph nyL yl Substituted particular examples given above, since numerous p yl a d alkoxyphenyl. to p c a mixture variations will readily occur to those skilled in of amines and ketones in which the amine is v'liich om rise subjecting a "mii giture or; a;

nitrool'efin of" aforesaid typeand an org darho izylic" acid having an ionization constant at toitheiaction of molecular hydroge'n in the: presence oi Ptaney' nickel catalyst atfeIevatedpressures and atem'perature of betweenabout 4 Q and 100 ,C., said reduction being carrie dout inthesubstantial absenc'e of'w'ater other than that formed by said reduction,

7. In a process for the reduction of nitroolefins of the type:

so; Ro=o-a1kyr wherein R"1'epresents a member selectedfrom the-"group consisting of alkyl, phenyl, a1k'yl-substituted phenyl andallcoxyphenyl, to produce a; mixture of amines'and ketonesin which the amine'is' present in predominating amounts, the

improvement which comprises subjecting amiX- turecontaining a nitroolefin of the" aforesaid type, an inert organic solvent other-than a water insoluble solvent, an organic carooxylic acid hav-" ing an ionization constantat 25 C; between-about- 1.4 X 10* and 1.86" 10 and 'lessjtha'n' about hydrogen-in the presence of Raney nickel catalyst at elevated pressures and in the presence of an inert organic solvent other than a waterinsoluble solvent andof an organiocarboxylic:

acid having an ionization constant ai -25f Q, oi between about l.l l0- and 1.l 1 0 said reduction being carried out in the absence of b waterother than that iormed by saidreduction.

9. In a process for the reduction of nitroole fins of the type:

No? a o 'c alliyi :i-" wherein R represents a member selected from the group consisting of alkyl, phenyl, alkyl substituted phenyl and alkoxyphenyl, to produce a mixture of amines and ketones in which the amine is present in predominating amountsthe improvement which comprises subjecting a mix-f ture consisting of a nitroolefin of the aforesaid type, an inert organic solvent other than a waterinsoluble solvent, and acetic acid and less than about one mole of water per mole of nitroolefin,

5." iifiib i nfih i rE5? ncejpf Raney" nickel catalyst at elevated pres e l. i l0, In a process for the reduction of nitro olefins of-the type:

NOE R n o-sun wherein Rrpieseiits a member selected from the" group con sistir'1'g' 0'f alkyl; phenyl, alkyl sub's'ti tu'te d" pheny-l and alkoxyphenyl, to produce" a" mixture" of arn'in'es and ketones in which the" amineis'pre's'ent in predominating amounts, the improvement which comprises subjecting a mixt'u'reconsisting of 'a"nitroolefin"of the aforesaidty'pe, analcohol solvent, and an-org'anicf cami boxylic acid" having an ionization constant at."

25 C. of betWeen' about LflXIO- and 1;1 10-' to the action of 'moleculai hydrogen in thef'pres ence of aaney nickel catalyst-at elevated pressureand "at"temperaturesbetween about 4'0" and 1091 0., said reduction being carried out inthe absence of water other than that formed by'said" reduction.

11. In a process for the preparation of lphenyl-Z-aminopropane'by the catalytic liquid phase reduction of phenyl nitropropenepthe improvement Which-comprises subjecting a'mixture' containing'phenyl nitropropene, anorganic solvent therefor other than a water insolubleisolventyand acetic acid and less than about"one mole of, Water per mole of'nitroolefin, to themtion of molecularhydrogen in thepresence of Raney nickel catalyst at elevated pressure.

12; In a process for the'preparation-of-2 a ninohexane by the j catalytic liquid phase re-' duction of 2-=nitro-'2-hexene, the improvementwhich comprises subjecting a mixture contain ing 'Z-nitrQ-ZmeXene; an organic solvent there-3 for other thana Water-insoluble solventyan'di acetic acid and'less' than about one mole'ofi Water per mole of nitroolefin to the-action of molecular hydrogen in the presence of Haney" nickel catalyst at elevated pressure.

JOHN B. TINDALL:

References-Cited in'thefileofthis" patent" UNITED STATES PATENTS;

Numbrfl a'me' Date 1,879,003 Alles Sept. 27, 1932 2,233,823 Susie et a1. 7 Mar. 4', 1941 2,35 ,532, Haffner et a1.- Aug; 22,1944 2,427,822 Tindall Sept. 23,1947

FOREIGN PATENTS. mater flour dry" Date 360,266 Great Britain Not f5, 1931 406,149 Germany Nov. 14, 1924 OTHER REFERENCES Schales et al., Ber. deut. Chem;', vol. 68, pp. 1579-1591 (1935).

Serf. No. 255,882, Haffner et al. (A. P. 0.), published April 20, 1943. 

1.IN A PROCESS FOR THE REDUCTION OF NITROOLEFINS OF THE TYPE: 